Skeletal Muscle Tissue Ch. 10-2 notes

Connective Tissue Components Fascia (fash-ee-a) – a sheet or broad band of C. T. that supports and surrounds muscles and other organs of the body 2 types Superficial and deep deep has 3 layers Epimysium (most superficial) Perimysium Endomysium (most deep)

Anatomy of Muscle Fiber Epimysium – outermost Perimysium – surrounds bundles of muscle fibers Endomysium – separates muscle fibers from each other

Microscopic Anatomy of a Muscle Fiber Muscles form from the fusion of myoblasts Once fusion occurs, the fiber can no longer divide Number of muscle fibers is set before birth The size of the muscle fibers is what changes over time

Components of a Muscle Fiber Sarcolemma – covering of muscle fiber that contains the nuclei Transverse (T) tubules – tunnel from surface toward center of fiber; carry action potential Sarcoplasm – cytoplasm of muscle fiber Contains myoglobin (binds oxygen to diffuse into muscle fibers)

Components

Components Myofibrils – contractile organelles of muscle fiber, little fibers stuffed into sarcoplasm Contain filaments Thin and thick Sarcoplasmic reticulum (SR) – fluid-filled system of sacs, surround each myofibril, stores Ca2+ for muscle contraction

Components Filaments – small structures within myofibrils Thick 2 thins for every 1 thick Arranged in sarcomeres Sarcomeres are separated by Z discs

Components Thin and thick filaments overlap Sarcomere can be divided into zones and bands A band – darker middle part of sarcomere Zone of overlap – where thick and thin filaments overlap I band – lighter, less dense area with thin filaments; Z disc passes through H zone – center of A bad with thick filaments M line – proteins hold the thick filaments together at the center of the H zone

Components

Muscle Proteins Myofibrils are built from 3 proteins Contractile – generate force during contraction Regulatory – help switch contraction process on and off Structural Keep thick and thin filaments in proper alignment Give myofibril elasticity and extensibility Link myofibrils to sarcolemma

Muscle Proteins Contractile proteins Myosin Actin Myosin and actin Form thick filaments Functions as a motor protein – push or pull structures to achieve movement 300 myosin form a single thick filament Actin Form thin filaments Each actin has a myosin-binding site

Muscle Proteins

Muscle Proteins Regulatory proteins tropomyosin Troponin Tropomyosin and troponin Part of the thin filament tropomyosin Covers the myosin-binding sites during the relaxed state Troponin Hold tropomyosin in place